STANFORD, California (CNN) -- The mouse that roared through the computer world turned 30 on Wednesday.

It was December 9, 1968, when inventor Douglas Engelbart unveiled the computer mouse, though no one called it by that nickname back then. Thirty years later, 200 million to 300 million mice are believed to be infesting the computer world.

Back when Engelbart introduced the mouse, it had a partner -- a five-key pad. His idea was that with the mouse in one hand and the keypad in the other, there would be no need for an ordinary typewriter-like keyboard.

Over the past three decades, the mouse has become standard equipment on more than 85 percent of computers, a fact Engelbart finds "mildly amazing." His keypad, however, went nowhere.

Perhaps that was because to replace the typewriter with the keypad, a computer user had to memorize 512 stroke combinations. The mouse, by contrast, just had to be shoved around on what has become known, appropriately, as a mouse pad.

The mouse got its nickname, in part, because of the cord that attached it to the computer, which looked like the rodent's tail. Today, though, some of the newest mice use wireless radio technology and have lost their tails.